In power cables having metal shields, it is advantageous to make the metal shield by longitudinally folding a metal tape around the core of the cable and leaving the seam of the shield as a lap seam with the edges free to move over one another circumferentially to accommodate expansion and contraction of the cable core with change in temperature. Power transmission cables are subject to substantial changes in temperature as the result of variations in the load on the cable from peak demand to slack loads when demand for electricity is low. In the usual construction, there is a plastic outer jacket extruded over the metal shield.
If the outer jacket adheres to the outside surface of the metal shield around the entire circumference of the cable, the stretching of the outer jacket, with increase in the diameter of the cable core by rising temperature, is concentrated at the region of the seam lap. In order to avoid excessive stretching of the outer jacket adjacent to the seam lap of the metal shield, bridging tapes which extend circumferentially in both directions beyond the outer lap of the seam, have been used. The outer extruded plastic jacket does not adhere to the bridging tape or the bridging tape is made of elastic material that stretches as the cable expands, and thus the stretching of the outer jacket is distributed circumferentially over the full width of the bridging tape.
This invention uses a bridging tape which is made of elastomeric material and which has a cross-section of different shape than those previously used; and these changes combine to provide a distribution of the stretch and a more streamline structure at the seam. The bridging element of this invention is made of relatively soft material which is thicker at the region of the outer lap of the metallic shield and with the thickness of the bridging element decreasing toward its longitudinal edges and preferably to a substantially feather edge.
Other objects, features and advantages of the invention will appear or be pointed out as the description proceeds.